The nucleus is the most important organelle in the proliferation, angiogenesis, and apoptosis of a cell (Zink, D. et al., 2004 Nat Rev Cancer 4, 677; Torchilin, V. P., 2006 Annu Rev Biomed Eng 8, 343). Controlling the functions of the nucleus in cancer cell growth and division has been the primary motivation for nuclear-targeted cancer therapy (Schwartz, G. K. et al., 2005 J Clin Oncol 23, 9408; Ashkenazi, A., 2002 Nat Rev Cancer 2, 420; Zaidi, S. K. et al., 2007 Nat Rev Cancer 7, 454; Munley, M. T. et al., 1999 Lung Cancer 23, 105). In conventional treatment, viral vectors are used for delivering drugs to cells (Lee, L. A. et al., 2006 Nanomedicine 2, 137; Douglas, T. et al., 2006 Science 312, 873). However, this approach results an immunogenic response in the hosts (Bertoletti, A. et al., 2006 J Gen Virol 87, 1439; Monahan, P. E. et al., 2000 Mol Med Today 6, 433; Kay, M. A. et al., 2001 Nat Med 7, 33). Over the past ten years, nanomaterials have offered a new type of delivery vehicle for targeted therapy because the drugs can be densely loaded on the nanocarrier, which simultaneously enhances the stability and pharmacokinetics of the molecules in vitro (Rosi, N. L. et al., 2006 Science 312, 1027). Although therapy using nanomaterials has started to be explored, most work has focused on only targeting surface receptors overexpressed on the plasma membranes to deliver drugs into the interior of the cancer cells (Davis, M. E. et al., 2008 Nature Reviews Drug Discovery 7, 771; Brannon-Peppas, L. et al., 2004 Adv Drug Deliver Rev 56, 1649; Gu, F. X. et al., 2007 Nano Today 2, 14; Shin, D. M. et al., 2008 Clin Cancer Res 14; El-Sayed, I. H. et al., 2008 Laser Med Sci 23, 217). Recently, nuclear targeting by peptide-modified gold nanoparticles has seen some success and shown improved anti-cancer efficacy (de la Fuente, J. M. et al., 2005 Bioconjugate Chem 16, 1176; Oyelere, A. K. et al., 2007 Bioconjugate Chem 18, 1490; Franzen, S. et al., 2003 J Am Chem Soc 125, 4700; Kang, B. et al., 2010 J Am Chem Soc 132, 1517). This therapeutic enhancement has been attributed to the interaction of the nanomaterials with the cancer cell nucleus. However, direct visualization of this interaction was not observed.
Both primary and metastatic tumors contain different subpopulations of cancer cells, i.e tumor heterogeneity (Dexter, D. L. et al., J Clin Oncol 1986, 4, 244-57; Shipitsin, M. et al., Cancer cell 2007, 11, 259-73; Swanton, C., Cancer Res 2012, 72, 4875-82). Tumor heterogeneity is one cause of drug resistance in cancer treatments. Current commercially available drugs rely on specific surface receptors of cancer cells, such as CD20 and epidermal growth factor, to increase therapeutic effects while reducing side effects in treated patients (Harris, M., Lancet Oncol 2004, 5, 292-302; Nahta, R. et al., Cancer Res 2004, 64, 2343-2346). One major issue of these treatments is that not all cancer cells in the same tumor express the target receptor. Hence, these treatments become cell-type dependent and frequently cannot eradicate the entire population of tumor cells (Brown, K. C., Current opinion in chemical biology 2000, 4, 16-21).
Nucleolin is one of the most abundant nucleolar phosphoproteins in the nucleus of a normal cell (Borer, R. A. et al, 1989 Cell 56, 379; Tuteja, R. et al., 1998 Crit Rev Biochem Mol Biol 33, 407; Ginisty, H. et al., 1999 Journal of Cell Science 112, 761). This protein is responsible for many cellular activities, including DNA transcription, cell proliferation, and cell growth (Srivastava, M. et al., 1999 Faseb Journal 13, 1911). In metastatic cancer cells and exponentially growing cells, nucleolin is overexpressed in the cytoplasm and translocated to the plasma membrane (Soundararajan, S. et al., 2008 Cancer Research 68, 2358; Soundararajan, S. et al., 2009 Molecular Pharmacology 76, 984; Hovanessian, A. G. et al., 2010 Plos One 5; Chen, X. et al., 2007 Molecular Therapy 16, 333; Ginisty, H. et al., 1999 Journal of cell science, 112, 761-772). Its trafficking ability has been implicated in transporting anti-cancer ligands from the cell surface to the nucleus. Thus, nucleolin has received attention for nuclear targeting-based therapeutics in conjunction with the single stranded DNA aptamer AS-1411 (26 mer, 7.8 kDa), which in its G-quadruplex homodimer form binds to nucleolin with high binding affinity (Kd is pM to low nM) (Mongelard, F. et al., 2007 Trends in Cell Biology 17, 80; Nimjee, S. M., 2005 Annu Rev Med 56, 555; Bates, P. J. et al., 2009 Experimental and Molecular Pathology 86, 151; Cao, Z. et al., 2009 Angew Chem Int Ed Engl 48, 6494). Aptamers, generally, are oligonucleotides that bind to specific moieties and act as targeting molecules, similar to monoclonal antibodies (mAbs). Aptamers, however, are smaller and less immunogenic than mAbs. AS-1411 (26 mer, 7.8 kDa) is a single stranded DNA that forms a G-quartet homodimer structure.
Binding of AS-1411 to nucleolin activates various biological cascades in cancer cells. One of the effects is destabilization of the anti-apoptotic bcl-2 mRNA. The degradation of bcl-2 mRNA subsequently triggers apoptosis in cancer cells. Although the testing of AS-1411 in clinical trials of myeloid acute leukemia and renal cell cancer is a positive sign of potential, there are concerns about the fate of the free drug in patients because of its fast clearance and pre-mature degradation before reaching the tumor (Stuart, R. K. et al., J Clin Oncol 2009, 27; Miller, D. M. et al., Ann Oncol 2006, 17, 147-148; Kim, B. Y. et al., The New England journal of medicine 2010, 363, 2434-43; Peer, D. et al., Nat Nanotechnol 2007, 2, 751-760).
It is therefore desirable to provide a method for transporting aptamers such as AP-1411 to a cancer cell for maximum anti-cancer effects. Such methods should not be specific to any one type cell, and indeed should be universal to many different cancer cell lines.